WO1988008757A1

WO1988008757A1 - Method for treating and/or coating nonwoven cellulosic substrates

Info

Publication number: WO1988008757A1
Application number: PCT/US1988/001591
Authority: WO
Inventors: Stephen L. Maher
Original assignee: Staley Continental, Inc.
Priority date: 1987-05-15
Filing date: 1988-05-13
Publication date: 1988-11-17

Abstract

Notable property improvements are obtained when nonwoven fibrous cellulosic substrates such as paper, paperboard, etc. are treated (e.g., size press treatment) with an aqueous solution of acrylamide-substituted starch materials and/or when said cellulosic substrates are coated with a pigmented aqueous coating composition containing the indicated starch materials.

Description

METHOD FOR TREATING AND/OR COATING NONWOVEN CELLULOSIC SUBSTRATES

Background of the I nvention This invention pertains generally to methodology for the treatment and/or coating of nonwoven, fibrous cellulosic substrates such as paper,

5 paperboard, etc. More particularly, such invention involves the use of treatment solutions and/or coating compositions containing an effective amount of certain acrylamide-substituted starch derivatives .

I n the manufacture of paper, starch and ■JO cationic derivatives thereof have long been used as additives in the wet end of the paper making process for such purposes as in compensating for poor refining or inadequate base fiber, to increase paper strength, to lay surface fuzz, to increase stiffness and/or rattle, to

15 retain inorganic fillers, and the like. I n addition, starch and various derivatives thereof have also been used extensively in the size press treatment of paper wherein a preformed web of the paper substrate is treated by applying an aqueous starch paste thereto,

20 squeezing excess starch paste from the paper substrate and drying the resulting treated paper product. Such size press starch treatments are typically done in order to improve appearance and erasability, to inhibit ink penetration and to form a hard firm surface for writing

25 or printing and in order to improve strength, reduce surface fiber picking, provide resistance to colloidal solutions such as blood and prepare the sheet for subsequent coating .

Starch and various starch derivatives are also

20 commonly employed as an adhesive component in pigmented paper coating compositions which are commonly referred to in the paper making art as "coating colors" and which typically contain relatively large amounts inorganic pigment materials such as clay, calcium carbonate, titanium dioxide, etc. Hydroxyalkylated starches such as, in particular, hydroxyethylated starch, having relatively low levels of hydroxyalkyl substitution (e.g. , from about 0.05 to about 0.1 hydroxyalkyl group per anhydroglucose unit) have been found to be especially well suited for use as adhesive ingredients within pigmented paper coating compositions.

One category of starch derivative which is known but which has not heretofore found use in the treatment or coating of nonwoven, fibrous cellulosic substrates such as paper, paperboard etc. are the starch acrylamide products described in U.S. Patent 4,060,506 to Verbanac (issued November 29, 1977) . Such products, briefly described, are derivatized starch materials which have pendant acrylamide functional groups of the formula

0 I I I I -N-C-C=CH₂ covalently bonded thereto. According to the indicated Verbanac patent, the starch acrylamide products of concern therein were especially designed, and are particularly well suited, for use as a synthetic polymer replacement in the manufacture of shaped (e.g. , molded, extruded, etc. ) articles and in the preparation of protective coatings for a variety of substrates such as textiles, papers, metals, wood, etc.

U.S. Patents, 4,079,025 and 4,115,332 to Young et al . employ the above-described starch acrylamide products to prepare, respectively, certain copolymerized starch compositions and certain water-rabsorbent copolymerized starch products by formulating said starch acrylamide materials in a controlled fashion with selected ethylenically unsaturated comonomer materials .

SUMMARY OF THE INVENTION

It has now been discovered that notable property improvements are provided when nonwoven, fibrous cellulosic substrates such as paper, paperboard, etc. are treated with an aqueous solution of, and/or are coated with a pigmented coating composition containing, the aforementioned starch acrylamide products . Accordingly, the present invention in one of its embodiments is a method of treating a nonwoven fibrous cellulosic substrate, said method comprising the steps of: a. applying an aqueous solution to said substrate, said solution comprising, on a total solution weight basis, from about 0.5 to about 35 weight percent of a starch acrylamide product which comprises a starch chain and appendant acrylamide groups contiguously attached to said starch chain with said appendant group being characterized as containing terminal

moieties; b. dewatering the resulting treated cellulosic substrate; and c. subjecting the resulting treated cellulosic substrate to a curing operation in which the starch acrylamide product is crosslinked by polymerization of the appendant acrylamide groups . In another of its embodiments, the present invention resides in a method of coating a nonwoven fibrous cellulosic substrate with a pigmented coating composition, said method comprising the steps of: a . applying a pigmented coating composition to at least one side of said cellulosic substrate, said coating composition being an aqueous dispersion comprising, on a total coating composition weight basis : i . from about 30 to about 80 weight percent water, ii . from about 10 to about 60 weight percent of a water insoluble pigment material, and iii . from about 0.5 to about 15 weight percent of a starch acrylamide product which comprises a starch chain and appendant acrylamide groups contiguously attached to said starch chain with said appendant group being characterized as containing terminal

0 -N-C-C=CH₂ moieties; b. dewateriπg the resulting coated cellulosic substrate; and c. subjecting the resulting coated cellulosic substrate to a curing operation in which the starch acrylamide product is cross!inked by polymerization of the appendant acrylamide groups.

Nonwoven , fibrous cellulosic products treated and/or coated in the foregoing fashion have been observed to exhibit unexpectedly improved tear strength and to exhibit significantly enhanced tensile strength ,

Mullen Burst values and Scott Bond test results relative to those of comparative counterparts treated and/or coated using a corresponding starch product not containing the requisite acrylamide functionality and also have enhanced water penetration resistance and oil holdout relative to their non-acrylamide comparative counterparts.

In a preferred embodiment hereof, the indicated starch acrylamide product has an acryfamide degree of substitution (acrylamide D. S. ) corresponding to an average of from about 0.01 to about 0.2 acrylamide groups per anhydroglucose unit in said starch product and further contains an average of from about 0.01 to about 0.2 hydroxyalkyl (especially hydroxyethyl) substituents per anhydroglucose unit. It is also generally preferred in the practice of the present invention that the aqueous treating and/or coating compositions employed be substantially free of (and preferably be completely free of) addition polymerizable ethylenically unsaturated materials other than the aforementioned starch acrylamide products.

DETAI LED DESCRI PTION OF THE I NVENTION

Starch acrylamide products suitable for use in accordance with present invention are those which comprise a starch chain having contiguously attached thereto appendant acrylamide groups of the formula:

0 -l.-(.-C=CH₂. Typically such starch acrylamide products will contain an average of at least one appendant acrylamide group for every 2000 D-glucose units within the starch chain (i . e. , an acrylamide D. S . of at least about 0.0005 per anhydroglucose unit) and will preferably have an acrylamide D. S . of at least about 0.001 . At the other extreme, such products may, if desired, contain as many as 500 of said acrylamide groups per lOOOD-glucose units withi.n the polymer chain (i . e. , an acrylamide D . S . of up to about 0.5 per anhydroglucose unit) .

Generally speaking, the starch acrylamide products suitable for use herein correspond to those which are described in U . S . Patent 4, 060,506.

Accordingly, the teachings of said patent concerning such products and concerning methodology for the preparation thereof is hereby incorporated by reference.

Illustrative polymerizable starch acrylamides may be represented by the structu ral Formula A;

R*0 R Starch D-Q- -ϋ -C=CH, (A) wherein starch represents a ^2j starch chain , R 1 is a member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, R represents a member selected from the group consisting of hydrogen and mono-organo group linked to alpha carbon atom of the -8-

ethylenically unsaturated group of the acrylamide moiety by a monovalent linkage, Q represents an organo group which dfvalently joints the D group with the acrylamide group; D is a member selected from the group consisting of sulfur and oxygen linking said Q group to the starch chain and "a" represents the number of acrylamide substituents per anhydroglucose unit of said starch molecule (frequently referred to in the art as degree of substitution or D.S. ) . Typically the individual appendant acrylamide groups will have a molecular weight of less than 400 and most typically said molecular weight will be in the range of from about 100 to about 200.

In Formula A, Q may be any divalent organo group which joins the acrylamide radical to the starch chain (e.g. , linked to D and acrylamide nitrogen atoms via carbon linkages) . The starch oxygen or sulfur atoms and acrylamide nitrogen atom may be directly linked together by a single carbon atom or an organo group comprised of a plurality of carbon atoms with the starch D and

groups of the acrylamide starch being divalently linked by different Q carbon atoms. The Q group may be comprised of substituted or unsubstituted straight or branched aliphatic groups (e.g. , alkylene) , substituted or unsubstituted arylene group (e.g. , naphthalene, phenylene, etc. ) as well as divalent organo groups which contain carbon to non-carbon atom linkages (e.g. , organo ethers and thioethers, sulfonyl, N-methylene substituted secondary and tertiary amines such as

CH₂-N(H)-Q-radical. The Q group linking chain may contain carbonyl, carbonylhydroxy, thiocarbonyl, etc. -9-

groups as well as monovalent substituents such as hydroxy, halo, (e. g . , Br, F, Cl and I) , alkyl, aryl, hydroxyalkyl, hydroxyaryl, alkoxy, aryloxy, carboxyalkyl, carboxyaryl, amine substituents, combinations thereof and the like. Advantageously the divalent Q organo group contains less than 10 carbon atoms and preferably no more than 7 carbon atoms . In Formula A, R and R may be members selected from the group consisting of mono-organo and hydrogen substituents . The R and R mono-organo group may contain an ester, ether, carboxylic, organo acid, alcohol, hydrocarbyl (e.g . , alkyl, aryl, phenyl, etc. ) groups as well as divalent organo groups containing non-carbon atom to carbon chain linkages

(e. g. , such as oxy, sulfonyl, thio, carbonyl groups, etc. as mentioned above with respect to Q) .

Advantageously R is either H or a substituted or unsubstituted mono-organo group containing less than 8 carbon atoms such as a lower alkyl or phenyl group.

Illustrative substituted mono-organo groups are halo substituted alkyl and phenyl, alkoxy, aryl, phenoxy, phenol and alkanol and correspondingly thiol, alkanoic, tolyl, benzoyl, carboxy, sulfoalkyl, sulfophenyl groups, combinations thereof and the like. I n the preferred embodiments of this invention, R and R are a member selected from the group consisting of either hydrogen or a 1 -5 carbon alkyl (preferably methyl) and "a" has a value of at least 0.001 . Preferably "a" has a value representing an acrylamide D . S . of from about 0.01 to about 0.5 and more preferably from about 0.01 to about

0.2. ln certain preferred embodiments of this invention, the starch acrylamides employed are represented by the formula:

H R 0 R Starch D (Q¹)_n-C-N-C-C=CH₂ (B)

H a

D is a member as defined above (preferably oxy) , Q represents a divalent organo group such as Q as defined above "a" represents the degree of substitution, R and R are monovalent groups as defined herein and "n" is an integer of 0 to 1 .

The starch acrylamides depicted by Formula B may be prepared by either reacting a starch or starch derivative containing the appropriate Q reactive moiety (if present) with the appropriate acrylamide reactant. Starch acrylamides which do not contain the Q moiety (i .e. , n is O) are typically prepared by reacting the starch with the appropriate

N-hydroxymethyl-acrylamide reagent. Starch acrylamides which contain the Q moiety are typically prepared by initially derivatizing the starch so that it contains a hydrogen atom active Q substituent and then

1 reacting the Q derivatized starch with an acrylamide which contains an N-methylol group (e.g. , etherification) . For example, etherification of a hydroxyalkylated starch such as hydroxypropyl starch ether or its corresponding polypropylene oxide ether with N-methylol acrylamide provides a starch acrylamide having a Q moiety which may be represented by the formula -CH₂-C(C_H3)H-O)_nl (CH₂C(CH₃)H-O-wherein n-_j represents the number of repeating propylene oxide units, (e.g. , for hydroxypropyl starch ether, n, would be zero with Q being -CH(CH₃ CH₂O-) . The Q moiety for the hydroxyethyl ether and its corresponding polyethylene oxides as well as other unbranched polyalkylene oxide starch ethers may be depicted by the formula

wherein n, is an integer of at least 2 and n~ represents the number of repeating starch alkylene oxide units (e.g. , for hydroxyethyl starch ether n« would be zero and n, would equal two) . Through appropriate selection of starch derivatives containing different Q substituents containing a reactive hydrogen atom, starch acrylamides containing a variety of different Q linking groups can be prepared via the N-methylol acrylamide reaction route.

The starch chain depicted in Formulas A and B represent unmodified or modified starches obtained from a variety of sources such as cereal, leguminous, tuber starches, etc. Illustrative starch sources include tapioca, corn, high-amylose starches (e. g. , corn, pea, etc. ) , sweet potato, waxy maize, canna, arrowroot, wheat, sorghum, waxy sorgum, waxy rice, soya, rice, pea, amylopectin fractions, amylose fractions, combinations thereof and the like. Starch acrylamide products based upon common (or "dent") corn starch as the starting material have been found to be particularly well suited for use in the present invention .

Especially preferred modified starch acrylamide products for use herein are those which are derived from hydroxyalkylated (especially hydroxyethylated) starch derivatives (particularly those based upon common dent corn starch) containing an average of from about 0.05 to about 0.1 hydroxyalkyl substituents per anhydroglucose unit. Preferably such products have an acrylamide D. S. of from about 0.01 to about 0.1 . -12-

The indicated starch acrylamide products can suitably be in ungelatinfzed cold-water insoluble form; in ungelatinized cold water soluble form; or in pregelatinized cold water soluble form as may desired in a given instance.

In using the above-described starch acrylamide products to treat a nonwoven fibrous cellulosic substrate, such starch acrylamide product is first solubilized in water to form an aqueous solution or paste thereof. Typically, such aqueous paste or solution will contain, on a total weight basis, from about 0.5 to about 25 weight percent of the indicated starch acrylamide product and will preferably contain from about 5 to about 20 (most preferably from about 10 to about 15) weight percent thereof. Generally, the indicated starch acrylamide solutions will have (and will be applied to the cellulosic substrate at) a pH of from about 4.5 to about 6.5 (more preferably from about 5.5 to about 6.5) .

The indicated aqueous starch acrylamide paste or solution will typically have incorporated therein an effective amount (e.g. , typically in the range of from about 0.0005 to about 0.35, preferably from about 0.005 to about 0.2, weight percent on a total weight basis) of a free-radical polymerization initiator to facilitate the subsequent curing of the indicated starch acrylamide product. Conventional free-radical polymerization initiators which are suitable for such purpose include organic and inorganic peroxides (e.g. , hydrogen peroxide, cumene hydroperoxide, caproyl peroxide) , persulfates (e.g. , ammonium, sodium or potassium persulfate), oxidation- reduction initiator systems (e.g. sodium bisulfite, thiosulfates, sulfites in combination with persulfates or peroxides, etc. ) azo initiators (e.g. , azo - 13-

di-isobutyronitrile) , and the like. Levels of such initiators corresponding to about 0.1 to about 1 weight percent based upon the weight of the starch acrylamide product itself are generally suitable for the present purposes.

The resulting paste or solution of the starch acrylamide product can then be applied to the cellulosic substrate to be treated by contacting said substrate with said solution or paste in any conventional fashion as may be convenient and/or dictated by practical considerations such as equipment availability and the like. Typically the application of said paste or solution is conveniently conducted in the context of a conventional tub sizing or size press operation in which the cellulosic substrate to be treated is immersed in, or is otherwise saturated with, the aqueous starch acrylamide treatment composition and is dewatered by passing the saturated substrate press rolls and drying (e.g. , air drying, oven drying, vacuum drying etc. ) the resulting treated substrate.

Typically, the aqueous starch acrylamide treatment composition will be applied to the cellulosic substrate at a treatment composition temperature of from about 35 to about 80°C (preferably from about 50 to about 60°C) .

The amount of starch treatment composition solids applied to (i . e. , deposited on and/or within and retained by) the cellulosic substrate during the indicated treatment is typically in the range of from about 0.5 to about 5 (preferably from about 1 to about 3 weight percent on a dry cellulosic substrate weight basis.

Curing of the resulting treated cellulosic substrate is usually conducted by heating the treated - 14-

substrate to a temperature of from about 75 to about 200°C (preferably from about 80 to about 120°C. Such curing operation can be conducted, as desired, as part of (e.g. , in conjunction with or during) the aforementioned drying operation or as a separate and distinct step in the overall operation.

As has been noted, one embodiment of the present invention resides in a method for coating a nonwoven fibrous cellulosic substrate with a pigmented coating composition containing the above-described starch acrylamide product as a key ingredient therein .

Paper coating pigments suitable for use in the indicated coating compositions include any of the water insoluble pigment materials which are commonly and conventionally employed for paper coating purposes. Such pigments can suitably be organic or inorganic in character and include commonly used materials such as clay (e.g. kaolin), talc, calcium carbonate, zinc oxide, barium oxide, titanium dioxide, zinc sulfide, diatomaceous silica, blanc fix, carbon black, calcium silicate, lithopone, yellow, brown, and red ochres, burnt umber, Venetian red, chrome yellow, cadmium yellow, Prussian blue, ultramarine, Hansa yellow, Hansa orange, phthalocyanine blue, and the like.

Typically such pigments wifl constitute from about 10 to about 60 (preferably from about 20 to about 60) weight percent of the total weight of the coating composition and water will constitute from about 30 to about 80 (preferably from about 40 to about 60) weight percent of the total weight thereof.

The above-described starch acrylamide product is advantageously employed within the indicated coating composition at a level ranging from about 1 to about 15 - 15-

(preferably from about 1 to about 10) weight percent of the total composition weight and one or more of the above-described free-radical polymerization initiators is typically included within said composition at a level corresponding to from about 0.1 to about 1 weight percent on a starch acrylamide product weight basis.

While it is generally most convenient to include the indicated polymerization initiator within the treatment and/or coating compositions of concern herein, it should also be noted that said initiator can, if desired, be separately introduced into the treated and/or coated substrate subsequent to the application of the treatment and/or coating composition and prior to, during or subsequent to dewatering and/or drying of said coated or treated substrate.

Any batch or continuous technique employed for preparing conventional paper coating compositions suitably may be used in the preparation of those of the present invention . For example, the pigment, starch acrylamide product and any additional solid adjuvants employed may be pre-mixed dry in a suitable blending apparatus, e.g. a ball mill to provide a formulation which then can be dispersed in water for use. Alternatively, the ingredients employed separately or in various sub-combinations initially may be dispersed in the water and thereafter blended together to provide the desired color dispersion .

In the ultimate coating color, the starch acrylamide product to be employed must be in gelatinized form. If the starch derivative employed is in pregelatinized form, it need only be dispersed in water and no special treatment is required . In instances where the starch acrylamide product employed is in cold - 16-

water insoluble granular form, a slurry of it must be cooked and converted to a paste. Pasting of such granular starch derivatives suitably may be carried out before or after they have been combined with the pigment ingredients in the color formulation procedure. Where desirable, hydrolysis^* or modification of the starch binder may be carried out simultaneously with such pasting treatments. As is known, this may be achieved by adding acid or enzymes to the starch coating slurry before cooking and/or using high temperatures, e.g. 212 to 350°F. , and/or high shear in the pasting step. Any of these techniques are useful to effect an adjustment (lowering) of the final coating color viscosity during the starch cooking step.

In accordance with conventional practice, adjuvants commonly employed in paper coating colors, including pigment dispersants (e.g. sodium hexametaphosphate) , pH adjustment agents (e.g. sodium hydroxide or calcium chloride) , soaps (e.g. sodium stearate), defoamers, preservatives, wet-rub improvement agents, and the like, also suitably may be employed alone or in combination in the paper coating compositions of the present invention . Care should, however, be exercized so as to not exceed a pH of about 7.5.

Coating compositions may be prepared in accordance with the present invention for use in any conventional coating equipment. Colors of the invention containing up to 50% total solids, for example, may be produced for application by size press, calender stack, brush coater, knife-edge coater, air-knife coater, spread-shaft coater, or reverse-roll coater. Colors of 50 - 17-

to 70% total solids can be produced for application by print-roll coaters and trailing-blade coaters .

Typically, the pigmented coating compositions (or coating colors) hereof are applied to the cellulosic substrate of interest in an amount corresponding to from about 2 to about 15 (preferably from about 5 to about 8) pounds of dry coating composition solids per side per 3300 square foot ream of the indicated cellulosic substrate.

As was the case in connection with the above-described treatment operation, the coated cellulosic substrate can conveniently be cured to crosslink the starch acrylamide product within said coating by heating said coated substrate to a temperature of from about 75 to about 200 (preferably from about 100 to about 150)°C. Additionally, said curing operation can be conducted as a separate step in the overall process or can be accomplished in conjunction with the drying of the coated substrate at a suitable elevated temperature.

As has been noted above, the treated and/or coated cellulosic substrates prepared in accordance herewith have notably improved physical properties (e. g. , strength, flexibility, etc. ) and enhanced oil holdout and water penetration resistance as compared to substrates coated and/or treated in a corresponding fashion using a comparable starch ingredient differing only in the respect of not containing the requisite acrylamide substituents .

The present invention is further understood and illustrated by reference to the following examples thereof in which all parts and percentages are on a weight basis unless otherwise indicated explicitly or by implication . EXAMPLE 1

In this example, a hydro xyethylated and acrylamidomethylated common corn starch derivative having a hydroxyethyl D. S . of about 0.05 and an acrylamidomethyl D. S. of about 0.025 is employed to treat a paper substrate made from a 50/50^* hardwood/softwood kraft furnish .

The aqueous starch solutions employed in the paper treatment are prepared by cooking same in a 20 percent starch solids aqueous dispersion for 20 minutes at 96°C. The resulting cooked starch paste are then diluted with cold water to the starch solids level desired for use in the paper treating operation . Such cold water dilution results -in a diluted solution temperature of about 65°C or less and 0.5 weight percent (based on starch) of ammonium persulfate is then added to the diluted solution as a curing catalyst.

The diluted treatment solutions are prepared at starch solids levels ranging, in 2 percent intervals, from 2 percent to 10 percent starch solids .

In initially preparing the paper substrate, a 50/50 blend of hardwood kraft and softwood kraft is employed; the Canadian Standard Freeness is approximately 400ml; 0.2 weight percent (based on pulp) of rosin size and 0.4 weight percent (based on pulp) of papermakers alum is included in the furnish; the pH is about 5.5; and a 0.6% consistency is achieved. The paper is made at a machine speed of approximately 750 ft. /minute and at a basis weight of approximately 40 lb./3300 square foot ream and the moisture content of the paper web at the size press is approximately 10 percent. - 19-

During the course of the paper treating operation (which is conducted simultaneously and in line with the paper making operation and using an in-line size press machine) the amount of hydroxyethyalted/acrylamidomethylated starch material applied to and retained by the paper substrate (i . e. , the starch material "add-on weight") is primarily determined by and dependent on the starch solids content of the treatment solution employed and ranges from 0.1 weight percent to 6.8 weight percent.

Curing of the hydroxyethylated/acrylamido- methylated starch derivative-containing paper substrate is accomplished by heating the treated substrate at a temperature of about 90°C for a time period of approximately 10 seconds.

For comparative purposes, a series of control experiments are conducted in accordance with the foregoing procedures except that a hydroxyethylated starch material is employed which has viscosity characteristics comparable to the aforementioned acrylamido-methylated derivative but which does not contain any acrylamidomethyl substituents .

The results of these experiments show that, at add-on levels of 1 .5 and 2%, the acrylamidomethylated hydroxyethylated starch derivative provide significantly enhanced Scott Plybond, Mullen Burst, Machine Direction (MD) Elmendorf Tear, Cross Direction (CD) Elmendorf Tear test results and enhanced stiffness, oil holdout and water penetration resistance characteristics relative to that which is obtained using the comparative hydroxyethylated starch material. -20-

EXAMPLE 2

In this example, a pigmented coating composition is prepared containing the following ingredients:

100 parts clay (pigment) 85 parts water 5 parts HE/A AM starch*

0.025 parts potassium persulfate

15 parts of a carboxylated styrene butadiene latex

0.1 parts glyoxal *A hydroxyethylated/acrylamido-methylated starch derivative having a hydroxyethyl D.S. of about 0.05 and an acrylamidomethyl D.S. of about 0.025.

In preparing the coating composition, the indicated starch derivative is first slurried at a 15 percent solids level in water and is cooked or pasted at a temperature of about 96°C for 20 minutes prior to being combined with the remainder of the coating composition ingredients. The cooked (pasted) starch solution is diluted in water to the solids desired for the aforementioned coating formula. Said dilution results in a coating composition temperature in the desired range for application to paper i.e. 50 - 65°C.

The resulting coating composition is then applied to a 50 pound per 3300 square foot coating raw stock paper substrate typically used in "web-offset" printing at a level of 8 pounds of coating composition solids per 3300 square foot using a paper coating machine in the flooded nip/blade metering configuration . This application was such that a speed of 750 feet per minute was achieved. In order to achieve the desired coat weight, the blade geometry of the metering station -21-

was set at 45 degrees for the coater head angle and 45 degrees for the blade tip angle. Such geometry is typical to the industry.

The cooked (pasted) starch solution is diluted in water to the solids desired for the aforementioned coating formula. Said dilution results in a coating composition temperature in the desired range for application to paper i.e. 50 - 65°C.

The resulting coated paper product is then dried and cured at a temperature of about 250°C.

For comparative purposes the foregoing procedure is repeated using an hydroxyethylated starch derivative (hydroxyethyl D. S . = 0.05) in place of the indicated HE/AMM starch derivative. _C. Comparison of the properties of the resulting coated paper products reveals that the product coated with the acrylamidomethylated starch derivative-containing composition has substantially better strength properties and printing characteristics than the comparative control product. 0

While the present invention has been described and illustrated by reference to certain specific embodiments and examples thereof, such is not to be interpreted as in any way limiting the scope of the

~r- instantly claimed invention .

30

Claims

What is Claimed is

1 . A method of treating a nonwoven fibrous cellulosic substrate, said method comprising the steps of: a. applying an aqueous solution to said substrate, said solution comprising, on a total solution weight basis, from about 0.5 to about 35 weight percent of a starch acrylamide product which comprises a starch chain and appendant acrylamide groups contiguously attached to said starch chain with said appendant group being characterized as containing terminal

moieties; b. dewatering the resul ti ng treated cel l ul osi c substrate; and c. subjecti ng the resulting treated cel l ul osic substrate to a curi ng operation i n whi ch the starch acryl amide product i s cross! i nked by polymerization of the appendant acryl amide groups.

2. The method of Claim 1 wherein the starch acrylamide product has an average of at least one appendant acrylamido group for each 1000 D-glucose units of the starch chain .

3. The method of Claim 1 wherein the appendant acrylamide group has a molecular weight of less than 400.

4. The method of Claim 1 wherein the acrylamide D. S. of the starch acrylamide product ranges from about 0.01 to about 0.2 and the individual appendant acrylamide groups have an average molecular weight ranging from about 100 to about 200.

5. . The method of Claim 1 wherein the starch acrylamide product comprises a starch acrylamide

wherein starch ^" represents a starch chain , R is a member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, R represents a member selected from the group consisting of hydrogen and mono-organo group linked to alpha carbon atom of the ethylenically unsaturated group by a monovalent linkage, Q represents an organo group which divalently joins the D group with the acrylamide group; D is a member selected from the group consisting of sulfur and oxygen, and "a" represents the number of acrylamide substituents per anhydroglucose unit of said starch molecule.

6. The method of Claim 5 wherein , in the starch acrylamide product of the formula A, D is an oxy group, Q is an alkylene moiety lin king the starch D group with the nitrogen atom of said acrylamide group and "a" represents a D . S . of at least 0.0005.

7. The method of Claim 5 wherein D is an oxy group, R and R are members selected from the -24-

group consisting of hydrogen and a monoorgano group containing less than 8 carbon atoms .

8. The method of Claim 7 wherein R is a member selected from the group consisting of hydrogen and methyl, R is hydrogen and "a" represents a D. S. ranging from about 0.01 to about 0.5.

9. The method of Claim 1 wherein the starch

w erein starc represents a starc chain, R is a member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, R represents a member selected from the group consisting of hydrogen and mono-organo group linked to alpha carbon atom of the ethylenically unsaturated group by a monovalent linkage,

Q represents an organo group which divalently joins the

D group with the acrylmide group; D is a member selected from the group consisting of sulfur and oxygen with D linking said Q group to the starch chain, "a" represents the number of acrylamide substituents per anhydroglucose unit of said starch molecule and "n" is an integer of 0 to 1 .

10. The method of Claim 9 wherein, in the starch acrylamide product of the formula B, "n" is zero and "a" represents a D. S . of at least 0.001 .

11 . The method of Claim 9 wherein D is any oxy group, R is a member selected from the group ccoonnssiissttiinngg of hydrogen and a lower alkyl and R is hydrogen ,

12. The method of Claim 11 wherein "a" represents a D. S . ranging from about 0.01 to about 0.2.

13. The method of Claim 9 wherein the starch acrylamide is characterized as forming a flowable starch acrylamide paste when one part by weight starch acrylamide is admixed with 100 parts by weight water at 95°C.

14. The method of Claim 13 wherein "n" is zero, D is an oxy group, R is hydrogen and R ^*is a member selected from the group consisting of hydrogen and methyl and "a" represents a D. S . of at least 0.001 .

15. The method of Claim 1 wherein the starch acrylamide product is derived from a hydroxyalkylated dent corn starch having a hydroxyal kyl D . S . of from about 0.01 to about 0.2.

16. The method of Claim 1 wherein from about 0.5 to about 5 weight percent of the acrylamide starch product is retained by the treated cellulosic substrate, said weight percentage being determined on an acrylamide starch product dry solids weight basis and on an initial cellulosic substrate dry weight basis .

17. The method of Claim 1 wherein the aqueous starch acrylamide treatment solution further comprises, on a total solution weight basis, from about 0.0005 to about 0.35 weight percent of a free-radical polymerization initiator and wherein the curing operation of step (c) is conducted by heating the treated cellulosic substrate to a temperature of from about 75 to about 200°C.

18. The method of Claim 17 wherein the free-radical polymerization initiator is ammonium, sodium or potassium persulfate.

19. A method of coating a nonwoven fibrous cellulosic substrate with a pigmented coating composition, said method comprising the steps of: a . applying a pigmented coating composition to at least one side of said cellulosic substrate, said coating composition being an aqueous dispersion comprising, on a total coating composition weight basis : i. from about 30 to about 80 weight percent water, ii . from about 10 to about 60 weight percent of a water insoluble pigment material, and iii . from about 0.5 to about 15 weight percent of a starch acrylamido product which comprises a starch chain and appendant acrylamide groups contiguously attached to said starch chain with said appendant group being -27-

characterized as containing terminal

0.

-W-A. CH '2, moieties; b. dewatering the resulting coated cellulosic substrate; and c. subjecting the resulting coated cellulosic substrate to a curing operation in which the starch acrylamide product is crosslinked by polymerization of the appendant acrylamide groups .

20. The method of Claim 19 wherein the starch acrylamide product comprises a starch acrylamide

R is a member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, R represents a member selected from the group consisting of hydrogen and mono-organo group linked to alpha carbon atom of the ethylenically unsaturated group by a monovalent linkage, Q represents an organo group which divalently joins the D group with the acrylamide group; D is a member selected from the group consisting of sulfu r and oxygen , and "a" represents the number of acrylamide substituents per anhydroglucose unit of said starch molecule.

21 . The method of Claim 20 wherein, in the starch acrylamide product of the formula A, D is an oxy group, Q is an alkylene moiety linking the starch D group with the nitrogen atom of said acrylamide group "a" represents a D. S . of at least 0.0005 and R and R are members selected from the group consisting of hydrogen and a monorgano group containing less than 8 carbon atoms.

22. The method of Claim 21 wherein R is a member selected from the group consisting of hydrogen a anndd mmeetthhyyll,, RR iiss hhyyddrrooggeenn aanndd ""aa"" represents a D . S ranging from about 0.01 to about 0.5.

23. The method of Claim 19 wherein the la:

is a member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, R represents a member selected from the group consisting of hydrogen and mono-organo group linked to alpha carbon atom of the ^* ethylenically unsaturated group by a monovalent linkage,

1 Q represents an organo group which divalently joins the

D group with the acrylamide group; D is a member selected from the group consisting of sulfur and oxygen with D linking said Q group to the starch chain, "a" represents the number of acrylamide substituents per anhydroglucose unit of said starch molecule and "n" is an integer of 0 to 1 .

24. The method of Claim 23 wherein, in the starch acrylamide product of the formula B, "n" is zero,

"a" represents a D. S. of at least 0.001 , D is an oxy g grroouupp,, RR is hydrogen or a lower alkyl group and R is hydrogen .

25. The method of Claim 24 wherein ""a_" represents a D. S. ranging from about 0.01 to about 0.2.

26. The method of Claim 19 wherein the starch acrylamide product is characterized as forming a flowable starch acrylamide paste when one part by weight starch acrylamide is admixed with 100 parts by weight water at 95°C.

27. The method of Claim 19 wherein the starch acrylamide product is derived from a hydroxyalkylated dent corn starch having a hydroxyalkyl D. S . of from about 0.01 to about 0.2.

28. The method of Claim 19 wherein the pigmented coating composition is applied, on a dry solids weight basis, to said cellulosic substrate in an amount corresponding to from about 2 to about 15 pounds per side per 3300 square foot ream.

29. The method of Claim 19 wherein the pigmented aqueous coating composition further comprises, on a starch acrylamide product weight basis, from about 0. 1 to about 1 weight percent of a free-radical polymerization initiator and wherein the curing operations of step (c) is conducted by heating the coated cellulosic substrate to a temperature of from about 75 to about 200°C.

30. The method of Claim 29 wherein the free-radical polymerization initiator is ammonium, sodium or potassium persulfate.